The present invention relates, in general, to semiconductor devices, and more particularly to semiconductor devices having bi-directional current blocking capability.
Many portable electronic devices use a lithium-ion battery as a power source. Lithium-ion batteries require a monitoring circuit to control the flow of current when the lithium-ion battery is used as a power source and when the lithium-ion battery is being charged. When in operation, the voltage potential across the battery must be monitored to ensure that the voltage potential of the lithium battery does not drop too low. If the lithium-ion battery is operated when the voltage potential of the battery is too low, the future performance of the lithium-ion battery can be degraded. Furthermore, lithium-ion batteries are very sensitive to the amount of current that passes through the battery when it is being charged.
Therefore, lithium batteries require a monitoring circuit that is both bilateral, allows current to flow in both directions, and that can withstand significant voltages while current is blocked in either direction. One way of providing this functionality is to place two n- or p-channel vertical field effect transistors in a back-to-back configuration so that they share a common source/drain.
Using two transistors in a back-to-back configuration has several disadvantages. Firstly, the channel region of two devices results in a higher on resistance in the current path. Secondly, the formation of two devices in a back-to-back configuration requires significant surface area, which results in a high die cost and an higher overall manufacturing cost.
Accordingly, a need exists to provide a semiconductor device that can operate bi-directionally and provide the necessary voltage protection when a lithium battery is in operation and when it is being charged. It would be advantageous if the semiconductor device can be formed using less surface area than traditional devices and using fewer processing steps.